1. Field of the Invention
This invention relates to electronic communication devices operating in a digital mode that reduce power dissipation.
2. Related Art
Portable electronic devices have become part of many aspects of personal, business, and recreational activities and tasks. The popularity of various portable personal electronic communications systems, such as portable phones, portable televisions, and personal pagers, is continually increasing. As the popularity of portable electronic systems increases, so does the demand for smaller, lighter, more powerful and more power efficient devices.
Amplification and processing of electronic signals is a function performed in many portable electronic systems. Amplification circuitry and semiconductor devices tend to generate significant amounts of heat and consume significant amounts of power. The continually shrinking packaging, containing the amplification circuitry and devices, has tended to reduce the ability of these devices to dissipate heat through convection. The space surrounding these devices has become significantly more confined as packaging sizes shrink, thereby reducing the opportunity for convection currents to circulate and remove heat. In addition the packaging for these smaller, lighter electronics devices is being made, in significant part, of materials such as plastics, that are generally lighter than metal packaging. Plastics, relative to metals, however, generally tend to have a greater thermal resistance to heat transfer. The opportunity for heat transfer, and the cooling of the power circuitry via conduction, may be significantly reduced by the increasing use of non metallic materials.
Reliability of a semiconductor device is generally directly related to the operating temperature of the device, as well as the change in temperature the device undergoes during it""s period of operation. For these and other reasons, manufacturers of portable electronic systems have sought to reduce power consumption of devices within their systems. By reducing the power consumption within their systems, the amount of heat generated is reduced and reliability is increased.
A benefit of reduced power consumption, in addition to increased reliability due to reduced temperature, is an increase in operational time. Because portable electronic devices are commonly battery powered, a reduction in power consumption may translate into a longer battery life and more time between recharges or battery changes.
One method of reducing power consumption is to employ digital designs. Digital communications systems are, in large part, replacing analog communication systems. One reason, that digital techniques have exhibited a rising popularity over analog systems is that digital systems may offer increased performance and lower overall power consumption than analog systems. Another reason that digital systems are increasingly popular is that digital systems generally may dissipate less power than their analog counterparts, in accomplishing the same functions. Digital systems may dissipate less power than analog systems because digital systems operate using two distinct values, often called ones and zeros. These values are generally created by semiconductors that are in the saturated state or the cut off state. In the saturation state, there is current flowing through the device, but the voltage across the device is low. Power dissipated in an electronic device is, for the most part, equal to the voltage across the device multiplied by the current flowing through it. The power dissipated by a device in the saturation state is the amount of current flowing through the device multiplied times a low saturation voltage. Because the saturation voltage of a semiconductor device is typically low, the power that is equal to the voltage times the current is also typically low. In the cut off state of a semiconductor device, the voltage across the device is usually at a maximum. In the cut off state the current through the device, however is typically low and is commonly zero or a low leakage current. Because the current is low in the cutoff state, the power that is represented by the current times the voltage is also typically low. Digital circuits are typically in either a cutoff or saturation state during operation, except for the times when they are switching between states. By contrast, analog circuits generally operate between the cutoff region and the saturation region, in an area commonly referred to as the active region. Devices that operate in the active region, generally have significant voltage levels across them and concurrently have significant current flowing through them. The concurrent presence of significant voltage and significant current, in a device that is operating in the active region, generally signifies that the product of the current and voltage, i.e. the power dissipated in the device, will also be significant. Devices, that operate in an analog mode tend to inherently dissipate more power than devices that operate in an digital mode. Thus, designers of power sensitive systems often employ digital circuits, if possible, as one method of saving power.
The first portable telephones created were analog systems. They tended to be large and require significant power sources. As portable designs continued to evolve, more and more phones were designed with an increasing number of digital circuits. While significant progress has been made in eliminating analog circuitry within phones, the conversion to digital circuits has not been 100% complete. There are still circuits that are analog or have significant analog components. In order to attempt further power savings manufacturers are continuing to attempt to replace analog sub systems with more efficient digital subsystems.
Power amplifiers, as used in portable communication devices, are commonly analog circuits that consume significant amounts of power. One embodiment of the invention employs a class D digital amplifier instead of an analog power amplifier. With a class D digital amplifier, a modification of the power output is achieved by changing the duty cycle of the amplifier. In this way the amplifier""s output may be changed depending on the output power requirement of the amplifier.
Portable communication devices typically have a significant amount of analog circuitry in for modulation. The modulation circuitry incorporates oscillators and linear phase shift circuits to accomplish signal modulation. This invention also employs a digital version of a phase shift modulator for providing phase shift keying modulation. Phase shift keying modulation within portable phones is often provided with circuitry containing a significant number analog elements.
A programmable divide modulator may be used to provide digital phase shift keying modulation. The programmable divide modulator is used, in the third embodiment, to replace circuitry containing analog elements. Because the improvements disclosed in the illustrated embodiments are primarily digital, power consumption may be reduced and reliability enhanced, compared with higher power consuming analog versions.
Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.